Electrolytic Generation of Manganese (III) Ions in Strong Sulfuric Acid

Abstract

An electrolytic cell and a method of electrochemical oxidation of manganese(II) ions to manganese(III) ions in the electrolytic cell are described. The electrolytic cell comprises (1) an electrolyte solution of manganese(II) ions in a solution of at least one acid; (2) a cathode immersed in the electrolyte solution; and (3) an anode immersed in the electrolyte solution and spaced apart from the cathode. Various anode materials are described including vitreous carbon, reticulated vitreous carbon, woven carbon fibers, lead and lead alloy. Once the electrolyte is oxidized to form a metastable complex of manganese(III) ions, a platable plastic may be contacted with the metastable complex to etch the platable plastic. In addition, a pretreatment step may also be performed on the platable plastic prior to contacting the platable plastic with the metastable complex to condition the plastic surface.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation-in-part of application Ser. No. 13 / 677,798, filed on Nov. 15, 2012, now pending, which is a continuation-in-part of application Ser. No. 13 / 356,004, filed on Jan. 23, 2012, now pending, the subject matter of each of which is herein incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates generally to an improved process for etching platable plastics such as ABS and ABS / PC.BACKGROUND OF THE INVENTION[0003]It is well known in the art to plate non-conductive substrates, (i.e. plastics) with metal for a variety of purposes. Plastic moldings are relatively inexpensive to produce and metal plated plastic is used for many applications. For example, metal plated plastics are used for decoration and for the fabrication of electronic devices. An example of a decorative use includes automobile parts such as trim. Examples of electronic uses include printed circuits, wherei...

AI Technical Summary

Benefits of technology

The present invention aims to improve the conditioning of plastic substrates before etching by providing an improved pretreatment step.

Problems solved by technology

However, only certain types of plastic components are suitable for plating.

One problem with the traditional chromic acid etching step is that chromic acid is a recognized carcinogen and is increasingly regulated, requiring that wherever possible, the use of chromic acid is replaced with safer alternatives.

The use of a chromic acid etchant also has well-known and serious drawbacks, including the toxicity of chromium compounds which makes their disposal difficult, chromic acid residues remaining on the polymer surface that inhibit electroless deposition, and the difficulty of rinsing chromic acid residues from the polymer surface following treatment.

Additionally, hot hexavalent chromium sulfuric acid solutions are naturally hazardous to workers.

However, none of these processes have proven satisfactory for various economic, performance and / or environmental reasons and thus none of these processes have achieved commercial success or been accepted by the industry as a suitable replacement for chromic acid etching.

In addition, the stability of these permanganate based etching solutions may also be poor, resulting in the formation of manganese dioxide sludge.

Thus formulations based on strongly acidic permanganate solutions are intrinsically unstable irrespective of whether the permanganate ion is added by alkali metal salts of permanganate or is electrochemically generated in situ.

In comparison to the currently used chromic acid etches, the poor chemical stability of acidic permanganate renders it effectively useless for large scale commercial application.

Alkaline permanganate etches are more stable, and are widely used in the printed circuit board industry for etching epoxy based printed circuit boards, but alkaline permanganate is not an effective etchant for plastics such as ABS or ABS / PC.

However, there is currently no suitable commercially successful etchant for plastics based on either permanganate (in either acid or alkaline form), or manganese in any other oxidation state or by using other acids or oxidants.